Patent literature 1 discloses a method and apparatus for producing a helical fastener element from a monofilament made of a synthetic resin. As shown in FIG. 2 of the patent literature 1, a monofilament 4 is supplied to a mandrel 21 and, based on the actuation of a screw 22 illustrated in two-dots broken line, the monofilament is helically wound about the circumference surface of the mandrel 21 along the axial direction of the mandrel 21. An engagement head is formed by an engagement-head shaping circular plate 23b, arranged adjacent to the mandrel 21, with the corporation of a die 23a. Additionally to this configuration, means for shaping a leg is provided in patent literature 1.
Patent literature 2 describes, at column 1, lines 65-67, that its one object to increase the flexibility of a slide fastener without lowing the strength of the slide fastener and, describes that a pair of monofilaments of oval shape are wound about a common mandrel so that their shapes are fixed, as an embodiment. The same literature describes, at column 3, lines 57-67, that the engagement element 12 is slightly longer along the longitudinal axis as shown in FIG. 13 of the same literature, describing that this is due to an apparatus for winding a coil. As would be understood from FIG. 2 and FIG. 24 of the same literature, a coupled portion 18 of one filament is disposed on another filament.
Patent literature 3 discloses a technique in which a fastener tape is weaved while a fastener element being incorporated into the fastener tape. As shown in FIG. 19 of the same literature, a shaping roll 118 which is for flattening a monofilament 106 of synthetic resin is incorporated into a loom. The same literature describes, at FIG. 13 and column 10, lines 7-10, that a monofilament of a circular cross-section is flattened successively by a rolling unit 15 such that a substantially oval cross-section is given thereto.
Patent literature 4 also discloses a producing technique similar to the patent literature 3.